[1] : The Collaborative International Dictionary of English v.0.48

opal \o"pal\, n. l. opalus: cf. gr. ?, skr. upala a rock,
   stone, precious stone: cf. f. opale. min.
   a mineral consisting, like quartz, of silica, but inferior to
   quartz in hardness and specific gravity.
   1913 webster

   note: the precious opal presents a peculiar play of colors
         of delicate tints, and is highly esteemed as a gem. one
         kind, with a varied play of color in a reddish ground,
         is called the harlequin opal. the fire opal has
         colors like the red and yellow of flame. common opal
         has a milky appearance. menilite is a brown impure
         variety, occurring in concretions at menilmontant, near
         paris. other varieties are cacholong, girasol,
         hyalite, and geyserite.
         1913 webster
see also:
precious opal harlequin opal fire opal common opal menilite cacholong 
girasol hyalite geyserite 

[2] : The Collaborative International Dictionary of English v.0.48

cacholong \cach"olong\, n. f. cacholong, said to be from cach,
   the name of a river in bucharia + cholon, a calmuck word for
   stone; or fr. a calmuck word meaning "beautiful stone"
   min.
   an opaque or milk-white chalcedony, a variety of quartz;
   also, a similar variety of opal.
   1913 webster

Cacholong >> C Words
Cacholong, definition of term: Cacholong
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